Process of molding balls



/NVENTOR CHARLES 1 F12 TH QMQGMLW fl-rrrozmgrs' C. v. FIRTH PROCESS OFMOLDING BALLS Flled Jmie 15, 1944 Dec. 3, 1946.

Patented Dec. 3, 1946 UNITED wm s PAT}ENT, orr cs raocsss or MOLDINGBALLS Charles V. Firth, Minneapolis, Minn., asslgnor,

by D y, sot-a mesne assignments, to Erie Mining Com- Hibbing, Minn., acorporation of Mine- Application June 15, 1944, Serial No. 540,522

i Claims. (Cl. 75- -3) This invention relates to a process of produc- IU ing pressure-hardened balls from pulverulent material at temperaturesbelow the boiling point of water. I

It is old in this art to introduce into a rotary I drum pulverulentmaterial and water for the purcal strength to be handled by standardequipment such as conveyers, cars, mechanical screens, bins, etc., withsubstantially no disintegration, deformation or packing.

In this novel process the whole of the pulverulent material is uniformlymoistened before introduction into the balling apparatus. Small nu 1 arehard and'smooth.

otherballs with the result that the molded balls An object of theinvention is to mold substan- 'tial balls of the desired diameterfrompulverulent material. I v

Another object is to mold pulverulentgmaterial I in an initiallymoistened state into pressure-hardened balls.

Other objects of the invention will become apparent from the followingdescription of a process and apparatus which exemplifies a preferredemclei are quickly formed and each nucleus rolls over a bed of moistenedpulverulent material and, in analogy to a rolling snowball, graduallypicks up molstenedsurface particles and attains the selectively desiredsize. A great difference in result over the older processes occursbecause the finally molded balls are relatively hard, tough and trulyspherical, quite uniform in diameter and possess considerable strengthand retention of form.

This radical difference in achievement of this novel process over theprior processes results from the fact that the new process is carriedout in such manner that the balls, as they are gradually being molded,exert a substantial'pressure upon a thin layer of moist particles whilerolling over them and adherently picking them up. For

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bodiment of the invention, the apparatus being diagrammaticallyillustrated in the accompanying drawing in which: I

, Fig. 1 is a vertical sectional view through the apparatus; r

Fig. 2 is a cross-sectional view on the line 2-2 of Fig. 1; s

Fig. 3 is a perspective viewof a portion of the interior face of amodified form of drum; Fig. 4 is a view similar to Fig. 2 but of amodified 'form, the rollers and gears being omitted;

Fig. 5 is a cross-sectional view on of Fig.4. v

It is to be understood that the invention is not to be considered aslimited by the disclosures herein made for the purpose of illustratingthe invention in such way that those skilled in the art may be enabledto practice, but it is to be considered as broader in scope andtoinclude such modifications, variations and changes as may fall withinthe scope of the appended claims. The pulverulent material to be moldedinto balls may be of difierent kinds, and for convenience ofexplanation, the invention will be detheline 5-5 scribed in connectionwith finely divided ironexample, in treating fine iron ores, the weightof I a rolling ball which has attained a one inch diameter amounts toapproximately .065 pound. The diameter of a spherical 200 mesh particleis .00291 inch' and therefore the area of the section through its centeris .0000067 square inch. Thus the pressure which may result from theweight of a one inch diameter rolling ball upon a single particle is inthe range of several thousand pounds per square men. It has been foundthat balls of magnetite iron ore molded by this process possess the samedensity and mechanical strength as would be secured by a pressure of15,000 pounds per square inch. The balls, as they form in' the rotatingdrum, are continuously abradlng one another. Any soft balls or looselyattached particles are quickly worn away and picked up by containingores.

There are-certain general requirements of the particle-size distributionthat is desirable in the pulverulent material for it to possess thenecessary properties for ball-molding by this process.

If it is desired to mold balls that are sufllciently substantial to besized on a mechanical screen and handled by standard mechanical meansprior to further processing, it is necessary that the pulverulentmaterial be made up of a wide range of particle sizes. Particlesentirely or largely of one size, although that size may be quite small,are not satisfactory. Material that could be classified as wholly sandyor granular" cannot be used in this process and neither could materialclassified as wholly colloidal. However, a

mixture of the two may be a satisfactory molding material. As anexample, satisfactory ball-mold- 3 ing has been secured with magnetitehaving the following size analysis.

Size v v f Coarscr than +38 microns Between 88 and +44 mierons Between44 and +20 m crons. Between 20 and l microns. Smaller than l0 micronstrate is eight per centum to eleven'per centum by weight of waterthoroughly mixed with the ma terial. A simple test for moisture-quantityis to take a handful of the moistened material and compact it or squeezeit. It should form a sub stantial compact but, if there is moisture leftin the hand when you release the compacted material, there is excessmoisture dispersed throughout the mass. Another test of proper moisturecontent is to drop the formed molded balls, as discharged from the rotardrum, upon a steel plate from a height of three feet. If too littlemoisture was present during formative period, then the balls willshatter, but if moisture content is proper, there will be only aperceptible flattening.

One suitable form of drum-ballin machine is shown in the accompanyingdrawing and in-- cludes an elongated metallic drum 4 mounted forrotation upon the pairs of idlers 5 and 6, which are positioned adjacentthe opposite ends of the drum. A convenient means for causing rotationof the drum is the provision of an annular gear 1 affixed to the outercircumference of the drum at one end. A pinion 8 meshes with the gear 1and the shaft 9 of the pinion is connected to a suitable source of power(not necessary to be shown). The drum may be slightly conical or ifcylindrical the axis should have a slight tilt from the upper feed endto the lower discharge end.

The degree of inclination of the drums inner surface to the horizontalis relatively slight and may be of the order of half an inch per foot,so that the balls being molded will migrate relatively slowly to thedischarge end.

This form of balling apparatus is old in the art but has not been highlysuccessful because it produces fragile masses of irregular shape, size,and density variously called glomerules, pellets, nodules, etc. It hasbeen discovered, however, that if means are provided whereby acomparatively thin, uniform layer of moist, pulverulent material ismaintained over the whole interior surface of the drum, an entirelydifferent balling action occurs that results in the produc-- tion ofalmost perfect spheres of uniform size. To accomplish this desiredeffect the inner face of the drum may be provided with a knurled surfaceIU as diagrammatically shown in Fig. 3, but it is preferred to provide aseries of spaced internal ribs II. In the drawing there are eight Iannular ribs shown in Fig. 1, but of course the number thereof may bevaried in accordance with the dimensions of the drum and the nature ofthe pulverulent material and the ribs may be longitudinal or acombination of annular and longitudinal. The height of each internal'rib ll may be one-fourth inch and the ribs spaced two and one-halfinches apart. The sole purpose of these ribs is to hold a thin layer ofthe pulverulent material firmly against the interior surface of the drumand any roughening of this interior surface that accomplishes thisresult is satisfactory.

In order to limit the thickness of the bed of the material adhering tothe inner surface of the rotary drum, a scraper blade I2 is suitablymounted upon a fixed support (not necessary to be shown) adjacent theopen feed end of the drum. This scraper blade inwardly extendsthroughout the major portion of the drum adjacent the inner face of thedrum opposite its upper travel. The top edge of this scraper bladeprojects about one-fourth inch from the top run of the drum ribs. Thescraper prevents the formation of a thick or irregular bed in theinterior of the drum, the scraped particles dropping downwardly to thelower run. I

In the form shown in Fig. 4, the feed hopper extends throughout themajor portion of the drum and the ore may be brought to, and distributedthroughout, the length of this hopper by a shovel or by a screw conveyeror belt conveyer or other common form of conveyer means, not necessaryto be shown. The bottom edge of this hopper 22 has an adjustable plate23 which regulates the thickness of the layer of the new ore added tothe inner surface of the drum. The hopper 22 may be convenientlysupported upon a channel iron 24 which extends through the drum and haseach of its ends maintained upon a suitable supporting structure notnecessary to be shown. The adjustable plate 23 is provided with aplurality of elongated slots 25 through each of which projects a stud 26aflixed to the inclined side of the hopper 22. A nut 21 is received andthreaded upon the end of each stud and when each nut 21 is turned down,the plate 23 will be held firmly in its adjustable position. The loweredge of the plate 23 is preferably spaced five-sixteenths of an inchabove the top faces of the ribs II. The adjustableplate 23 controls theinitial thickness of the bed of material as the material is being addedto the interior of the drum, while the scraper blade l2 also cooperatesin maintaining the smoothness and thickness of the bed of material. Theparticles scraped oil by the scraper l2 drop to the lower run of thedrum and form nuclei about which the balls quickly form. The form ofapparatus shown in Fig. 4 fulfills the requirements above discussed;however, it has been found simpler to make a mechanical drum as '-shownin Fig. 1. In this drum the ore is fed into the upper open end throughthe feed spout 24.

The ore and any re-cycled under-sized balls The scraper blade l2 assuresthe formation of a comparatively smooth bed of material of controlledthickness and the particles scraped from the upper run of the drum dropand form nuclei. The form of apparatus shown in Figs. 1 and 2 has provedto be commercially practical and its scum-c inch. The forming mu mresults approximate the results of the apparatus Q ring i3 whichmay besimilar to the annular.

ribs II but is of increased height, such for example, as two or threeinches. This retaining ring will hold the balls being molded for aslightly longer time than would be the case if the retaining ring wereomitted.

At the discharge end of the drum, beyond the retaining ring, it may bepreferable to provide an unribbed portion of the drum from which theformed balls are discharged. In this unribbed portion of the drum belowthe retaining ring the balls rolling directly on the drum surface do notgrow materially hardened and the balls obtain shape.

Because all molded balls do not grow at the same rate, it may bepreferable in order to pro-' duce uniformity of size to separate them byscreening. In the diagrammatic disclosure of the apparatus, the ballsroll down the chute H to the upper large screen 15 whose mesh may bevsuch as to cause balls having a diameter larger than the desired size tobe discharged to the floor or to a receptacle from which they may bereturned to the pug mill for reduction and re cycling. Those balls whichdrop through the upper screen I5 are received by the intermediate screenIt which has a smaller mesh and from which the rolling balls of thedesired size drop to a receptacle II for recovery while the undersizedballs, passing through the intermediate screen 18, will drop to thesolid base l8 and be delivered to the receptacle- I! for under-sized atruly spherical balls. As usually operated, the proportion of over-sizedballs ,is small but the proportion of under-sized balls is large, 50% ofthe weight not being considered excessive. These small balls arereturned directly to the upper end of the drum. They circulate throughthe drum and the in size but 'the ball-surface is screen until theyacquire the desired size. Re-

cycling of small balls is a desirable operating condition because thismeans that the balls are growing slowly in diameter which is a desirablefactor in the production of firmly molded balls.

For convenience, in case an operator hasinadvertently not impartedsufilcient moisture to the initial particles as they enter the rotarydrum, a small amount of water may be added through an atomizer.

In the carrying out of this novel process, it is essential that theballs grow slowly and gradually migrate to the lower end of the drum,rolling over the bed of damp particles which coat the interior of thedrum and whose thickness is limited by the overhead scraper. The speedof a three foot drum may be of the order of twelve to fifteen R. P. M.,but may be varied in accordance with the nature of the material treated.Initially at the feed end of thedrum, many fine particles will startrolling over the damp bed and will slowly grow in size by pickingmp theother particles much in the ing snowball in damp snow. The gradualmigration is imparted by the axial tilt of the drum downwardly to thedischarge end. As 'above pointed out in connection with the balling offine particles, the forming 1 balls exert increasingly greater pressurein rolling over the particles as theyarepickedupandthe exertedpressuremay bsottheorderofseveralthousandpoundsper manner of the growth of arollfeet diameter revolving at 12-15 R. P.

other and loosely attached particles are quickly worn away and picked upby other balls. The result of this is the production of molded ballsthat are hard and smooth and approach perfect spheres.

What I claim is:

1. Process of molding balls from moistened, finely divided ore materialwhich comprises providing a supply of said finely divided ore materialhaving a considerable range of particle sizes including a largeproportion of particles smaller than 44 microns diameter, and uniformlymoistened with from about 8 to about 11 percent by weight of water,maintaining an adherent layer of the uniformly moistened materialagainst the inside surface of a rotary drum, continuously scraping theformed layer to a smooth even surface, in uncompacted nuclei of saiduniformly onto said layer, a slow rotary movement thereby causing thefed material to migrate and the discrete nuclei to roll over the surfaceof the supported layer and slowly to grow into dense mechanically strongballs by the gradual accretion of moist particles thereto, terminatingrelative movement between the adherent layered material and the loosematerial when a portion of said nuclei have grown into balls having adesired size and a portion of said nuclei have grown into balls smallerthan said desired size, separating the undersized balls from the ballsof desired size, and using the undersized balls as added discrete nucleiin a repetition of the accretionary procedure.

2. The process defined in claim 1, characterized in that the relativemovement of the adherent layered material and the loose material isterminated when substantially half of the balled-up material resultingfrom any single cycle consists of undersized balls which are re-cycledfor further growth. I

3. The process defined in claim 1, characterized in that the rate oftravel of the rotary drum surface is equivalent to that of a drug ofthree '4. Process of molding balls from moistened, finely divided orematerial which comprises providing a supply of said finely divided orematerial having a considerable range of particle sizes including a largeproportion of particles smaller than 44 microns diameter, and uniformlymoistened with from about 8 to about 11 percent by weight of moisture,maintaining an adherent layer of the moistened ore material over theinterior surface of an inclined rotary drum, continuously scraping thelayer to a smooth even surface, feeding discrete nuciei of saidmoistened ore material onto said layer at the upper end of said drum,rotating said drum at a rate of travel equivalent to that of a drum ofthree feet diameter revolving at 12-15 R. P. M., thereby causing thenuclei to roll over the surface of the layer and slowly-to grow intodense mechanically strong balls by the gradual accretion of moistparticles thereto, continuously replacing moist .ore material removedfrom the'surface of said layer by the each" subjecting the supportedlayer to,

